Choke valves for use in the downhole environment of oil wells are well known. However, it is difficult to design and construct choke valves that fit within the restricted available space, that operate using limited power and that have long operational lifetimes. These choke valves must control the flow rate from high pressure oil reservoirs in the presence of fluids that contain abrasive particulate material such as sand, possibly in significant concentrations.
The above referenced U.S. patent application Ser. No. 14/174,575, whose disclosure is incorporated herein by reference in its entirety, describes a flow control valve that operates in a high-pressure environment to provide a controlled flow rate, while using limited power and limited space, and providing a long operational lifetime. Such flow control valve consists of a digitalized flow control valve with multipath and multistage pressure reduction structures. Specifically, the valve is configured as a set of parallel flow paths from an inlet (e.g. open to a formation containing a fluid) to an outlet. A choke valve controls the total flow rate by digitally opening different paths or different combination of the paths. Each path is controlled by a poppet cap valve that is basically operated in ON-OFF states. The number of flow states can therefore be up to 2N (2 to the power N), where N is the number of flow paths. In an exemplary non-limiting case where N=2 and two poppets p1, p2 are used to control flow of the two paths, 22=4 flow states are available, defined by the following configuration of the two poppets: (p1, p2)={(ON, ON), (ON, OFF), (OFF, ON), (OFF, OFF)}. To avoid erosion from sand in the fluid and high speed flow, the seal area of the poppet cap valve is located at a distance from the flow inlet away from the high speed flow and the speed is controlled to stay below a predefined erosion safe limit. Each flow path is a multistage structure composed of a set of serial nozzles-expansion chambers that equally distribute the total pressure drop to each stage. The pressure drop of each stage and, therefore, the flow speed at the nozzles and expansion chambers is controlled by the number of stages of the multistage structure. The flow paths have a relatively small cross section and could be relatively long for large number of stages and still fit in a strict annular space limit.
A choke valve, such as one described above, may be subject to positive or negative high pressure differential between its inlet and outlet ports which in turn can contribute to an undesired backflow of the fluid from the outlet of the choke valve to the inlet. There is a need for improved valves for control of flow in oil production to prevent such undesired backflow while maintaining the mentioned choke valve design goals.